Hideki Yagita

Novel High-Performance N-AlGaAs/InGaAs/N-AlGaAs Pseudomorphic Double-Heterojunction Modulation-Doped FETs

High-current driving pseudomorphic N-AlGaAs/InGaAs/N-AlGaAs double-heterojunction modulation-doped FETs (DH MODFETs) with high K-values have been successfully fabricated using an improved layer structure. The structure has been made by simply incorporating a thin N-AlGaAs layer at the heterointerface between the InGaAs and GaAs buffer layers of a conventional GaAs/InGaAs/N-AlGaAs pseudomorphic MODFET structure. A very high transconductance of 835 mS/mm and a K-value of 698 mA/(V2mm) were achieved at room temperature for a 0.35 µm-gate FET. Microwave results showed an fT of 64 GHz.

Direct measurement of the optimum source impedance for minimum noise figure

A novel measurement system and a method designed to measure the optimum source impedance for the minimum noise figure of an on-wafer FET have been developed using a microwave wafer probe system. The measurement system is composed of a network analyzer, a noise meter, microwave wafer probes, and coaxial switches that connect all three. The source (or load) impedance is measured continuously and the noise and gain characteristics of the transistor on the chip can be measured continuously and automatically as well. The optimum source impedance is measured by two different methods: the real-time method and the 50-short-open method. The two methods show little phase difference. This approach was used to design a low-noise MMIC (monolithic microwave integrated circuit) amplifier operating at 12 GHz.<<ETX>>